(1) Field of the Invention
This invention relates to a method of forming double layer attenuating phase shifting masks and more particularly to the use of a pellicle to restrict the formation of resist material to particular regions of the mask.
(2) Description of the Related Art
U.S. Pat. No. 5,382,483 to Young describes phase shifting masks using patterned opaque material on a transparent substrate with phase shifting spacers formed at the sidewalls of the patterned opaque material. Self alignment methods are used to form the phase shifting spacers.
U.S. Pat. No. 5,272,024 to Lin describes a method of repairing missing or unwanted phase-shifting elements in a phase shifting mask. First, second, and third phase shifting layers are deposited having phase shifts of .theta., 2.pi.-.theta., and .theta.. Repairs are carried out by removing one or two layers of phase shifting material.
U.S. Pat. No. 5,503,951 to Flanders et al. describes an attenuating phase shifting mask and a method of forming the attenuating phase shifting mask. The mask has recessed attenuating regions relative to the fully transmissive regions.
The Invention disclosed in this Patent Application describes a method of forming double layer attenuating phase shifting masks. An attenuating phase shifting layer is patterned to form an attenuating phase shifting pattern. An opaque layer is used to form alignment patterns for aligning the mask to the semiconductor wafer. A pellicle is used to provide a method having relaxed constraints on resists used in forming the mask and improved cleaning capability between critical fabrication steps.